Released in 1975, the Interton Video 2000 is one of the earliest german PONG systems. A few other systems like the Magnavox Odyssey, the Videomaster Home T.V. Game and the Video Sport MKII were released in 1974 in the UK (and other european countries for the two first ones), but the Video 2000 was a very advanced system for its era. Dedicated PONG chips did not exist yet, so CMOS chips were used instead. The system contains 14 CMOS chips that draw the basic graphic objects (players, central line and ball), and produce sound effects. In other words, the circuits of the system do what all the games have in common.
The main advantage of this system was the use of cartridges, which allowed playing PONG variants like Super Tennis (Cartridge 5) which displayed the scores using two rows of squares. More complex games could be played because the cartridges could also produce additional graphic objects. This system grades between the Odyssey (which uses cartridges to configure its internal circuits) and later advanced systems like the Philips Tele-Spiel ES-2201 whose cartridges contain additional components that add various game features.
Only five different cartridges are known to exist, yet the Video 2000 box shows two more games: Car Race and Naval Battle. These two games are much more complex than PONG games, and require much more complicated circuits, which could be the reason why they were possibly never released. However, a Video 2000 clone was made in Spain: Tele-Tenis, which also shows these two games. It is not known whether these games were released or not.
Technically, the cartridges configure the games by enabling the required graphics and by setting their size. They can also draw additional graphics like scoring. They also configure the game rules, for example the collision management, etc.
Amazingly, the Video 2000 powers automatically when a cartridge is inserted. A gray knob located near the cartridge slow can be used to tune the video signal, thus allowing fine-tuning on the system instead of the TV. Modern TV sets can easily catch the video signals with this clever feature (Philips Tele-Spiel systems also had this feature).
The two controllers use two knobs for moving the players horizontally and vertically. A push-button can also be used for the serves, or for shooting in the more advanced games like Naval Battle.
Video 2000 cartridges known to exist (click labels for more details):